Magnetisable material for detecting and/or recording electromagnetic radiation and electrons

ABSTRACT

WHERE 0 &lt; OR = delta &lt; AND 0 &lt; OR = E &lt; 1, B and B1 are bivalent Ni, Zn, Co, Mg, Mn or (LiFe) 0.5 and mixtures thereof, A and A1 are metals having a valence unequal to three, and Z is trivalent Co, Mn, or Cr and combinations thereof.   A device for detecting and/or recording electron and electromagnetic radiation employing as an active element a material having a magnetic parameter such as coercivity, permeability or magnetic permeability which changes upon exposure to such radiation. Materials suitable for this purpose are Y3Fe4.90Nb0.1 012, mixed crystals of (NiZn) Co204, and (NiZn) Fe204, and mixed crystals of

United States Patent Verhulst et al. 45 A 7, 1973 MAGNETISABLE MATERIIAL FOR 3,567,946 3/l97l Paul 250/833 R x DETECTING AND/0R RECORDING OTHER PUBLICATIONS ELECTROMAGNETIC RADIATION AND Teale et al. Chem. Abstracts," Vol. 70 pll9638z, ELECTRONS 1969, Page 374. [75] Inventors; Antonius Gerardus H ndrik Verweel Proc. Inst. of Elec. Engineers" PtBl09,

Verhulst; Theodoor Holtwijk; Suppl. No. 21, pages 95-98, Jan. 1962. Willem Lems; Ulrich Ernst Em, all of Emmasingel, Eindhoven, Primary Examiner-Archie R. Borchelt Netherlands Atmrney-Frank R. Trifari [73] Ass|gnee: Philips Corporation, New York, ABSTRACT A device for detecting and/or recording electron and [22] Filed: 7! 1972 electromagnetic radiation employing as an active ele 2 APPL 2 22 ment a material having a magnetic parameter such as coercivity, permeability or magnetic permeability Related Appllcamm Data which changes upon exposure to such radiation. Mate- [63] Continuation of Ser. No. 94,900, Dec. 3, 1970, rials suitable for this purpose are Y Fe Nb 0, abandonedmixed crystals of (NiZn) C0 0 and (NiZn) Fe 0 and mixed crystals of [30] Foreign Application Priority Data Dec, 6, I969 Netherlands 6918364 BFe2 5 E3+FeE2+O4 and BlZ2 8 EAHsZEHEQ1 U-S- CL viii-4:22:-"2::iwggg ljzLL a. Emmi m A 7' V [51] Int. Cl. 60] 1/00 where O s 8 and 0 S E l, B and B, are bivalent [58] Field of Search 250/83 R, 83.3 R Ni, Zn, Co, Mg, Mn or (LiFe) 0.5 and mixtures thereof, A and A are metals having a valence unequal to three, [56] References Cited and Z is trivalent Co, Mn, or Cr and combinations UNITED STATES PATENTS thereof- 3,4l9,496 12/1968 Vassiliev et a! 252/6257 1 Claim, 3 Drawing Figures ELECTRON 8EAM SOURCE -l DEFLEC'i'lON MEANS ANALYZER PAIENIEUMIB 1W 3.751.663

MEI 1 OF 2 I 3 yo 16-\ tz-U Fig.2

INVENTORS ANTONIUS G.H.VERHULST, THEODOOR HOLTWIJK, BY WILLEM LEMS and ULRICH E. E flaw/a K.

AGENT PATENTEU 7 SHEET 2 BF 2 ELECTRON BEAM SOURCE MEANS DEFLECTION ANALYZER magnetic permeability, can be varied by exposure to electrons or electromagnetic radiation. This variation is permanent below a temperature characteristic of the material in question. The initial condition can be restored by heating the material to above its characteristic temperature.

A material which, upon exposure to electromagnetic radiation, shows the above-described effect is known from the Dutch patent application No. 6,812,542 laid open to public inspection which is based on the discovery that for a material to show the above-described effect it must consist of a compound which contains two types of like magnetic ions in one type of which a weakly bound electron is in a condition which differs energetically from that in which a weakly bound electron is in the other type, while between said conditions there is an energy threshold present for the electron which, by exposing the material to electromagnetic radiation or electrons, can be exceeded. It is to be noted that it has also been found that exposure to electrons can produce a variation in the said magnetic properties.

It has been found in particular that the coercive force of such materials is increased by exposure to radiation while the permeability is reduced. Such an effect may be used as a base for a quite new system of magnetic recording.

For example, a layer of the material in question can be magnetized in one direction, then be exposed selectively (that is to say according to a given information pattern), and after the exposure be transferred to a magnetic field the field strength of which is smaller than the coercive force of the exposed parts but larger than that of the unexposed parts, and the direction of which differs from the first provided direction of magnetisation. In this manner the coercive force pattern obtained by exposure and consisting of regions having different coercive forces is converted into a magnetisation pattern consisting of regions having different magnetisation directions. This magnetisation pattern can be made visible, for example, by means of the magnetooptic Kerr effect. By using polarized light and observing th picture reflected by the layer via an analyser, the magnetisation pattern is then seen as a brightness pattern. I

The effect of exposure on the magnetic permeabilitymay also be used. A material according to the invention may then serve as a material for the core of the coil in an LC-circuit so that the natural frequency of the circuit varies by exposure. Such a circuit may be used as a dosimeter in which the quantity of incident radiation is measured by measuring the variation of the natural frequency.

The present invention relates to new materials which show the above-mentioned effect and which can be used in systems of magnetic recording and of detection, for example, as described above.

According to a first aspect, a suitable material for a device according to the invention consists of a compound of the formula 3 52.r u l2-z where R is an element of the rare earths or yttrium or a combination thereof and where A is a metal having a valency unequal to 3, while 0 1,0 s y land0 s l.

In a preferred embodiment a suitable material consists of a compound of the above-mentioned type of the formula.

In another preferred embodiment the material consists of a compound of the above-mentioned type of the fonnula Another material consists of a compound of the formula:

MgF rs )0.05 4

Yet another material consists of a mixed crystal having the composing compounds:

(NiZn),Co,O

and

(NiZn),Fe O

It is to be noted that it has been found that the mixed crystals described here present the advantage, as compared with the so far known compounds or the compounds mentioned hereinbefore, that the magnetic properties can be varied permanently by exposure to radiation at a temperature of 200 K. Such a variation has so far been found only at temperatures below K. The invention will now be described in greater detail with reference to the accompanying drawing in which FIG. 1 is a graph showin the change in permeability upon exposure to radiation of the active element of a device according to the invention;

H6. 2 are hysteresis loops of an active element of a device according to the invention;

FIG. 3 is a diagrammatic showing of a device according to the invention.

In the graph shown in FIG. I it is shown how the magnetic initial permeability, measured at a frequency of 10 kc/s, of a ring having a diameter of 0.25 cm and a thickness of 0.03 cm and manufactured from respectively.

a ms oms n decreases after the beginning of the exposure at the instant t 0. In all three cases exposure was carried out with light having a wavelength of 1.5 and the intensity measured at the surface of the ring was 10 W/sq.cm. The experiments were carried out at a temperature of 77 K.

In the graph shown in FIG. 2, reference numeral 1 denotes the hysteresis loop measured in a mixed crystal having the composing compounds h z 4 (P) and (NiZn) Fe O, (q)

in the dark at a temperature of 203 K, and reference numeral 2 denotes the hysteresis loop measured after the specimen had been exposed to the light of'a wavelength of 1.5 [1-, the intensity of the light beam measured at the surface of the specimen being W/sq.cm. The ratio p q was here I P: 99.

It is to be noted that effects as shown in these graphs have also been measured upon exposing the specimens in question to electromagnetic radiation having wavelengths shorter than L5 s infrared), notably white light and X-ray radiation. In addition it has been found that a decrease of the initial permeability and an increase of the coercive force can also be produced by exposure to electrons (B radiation).

In FIG. 3 an active magnetic element, i.e. an element a magnetic parameter of which can be changed by electron irradiation is shown at 5. The thickness of the element is such that the material is sufficiently transparent for the electron beam 2 which is produced by a source 1. The beam 2 which is produced by th source 1 impinges on the active element 5 by way of deflecting means 4 (an electro-magnetic or electrostatic) for defleeting the beam in a direction perpendicular to the plane of the drawing and by way of a lens 3. The element 4 enables the beam to be localized on the active element 5.

Surrounding the element 5 is an electromagnet 6 which can be energized to produce a magnetic field at right angles to the element 5.

After the element 5 has been given a degree of magnetization perpendicular to its plane, irradiation of the element will locally change the degree of magnetization. Thus, there is formed an image" in terms of the component of magnetization perpendicular to the plane of the element. It is noted that by moving the magnetic element sample, or many small samples, past the radiation beam a continuous recording somewhat similar to a magnetic tape would be obtained.

Read-out is effected by means of a source 9 of a linearly polarized light beam and a lens 10. The reflected light beam is observed by means of lens 7 and analyzer 8, the electron radiation produced by source 1 thus being converted into visible radiation.

What is claimed is:

l. A device for detecting and/or recording electron and electromagnetic radiation comprising an active element a magnetic parameter of which can be changed by electron and electromagnetic radiation, means to expose said element to said radiation, and a magnetic detector to observe the magnetic parameter change, said active element consisting essentially of a ferromagnetic material selected from the group consisting of Y Fe Nb ,O, and mixed crystals of (NiZn) Co O,and (NiZn) Fe Q 22 33 UNITED STATES PATENT m CERTIFICATE OF CORECTIUN Patent No. 3,751,663 Dated August 7, 1973 Inventor(s) ANTONIUS G. H. VERHULST ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

I' y "W Col. 1, line 53, change "th" to read -the-. Col. 3, line 10, change "1.09" to read --l.90 Col. 3, line 33, lelete "P" si gnedta nd sealed this 27th day of November 1973.

(SEALI. Attestz EDWARD M.PLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

